1. Field of the Invention
This invention relates generally to tracking control systems for magnetic recording and reproducing systems and, more particularly, is directed to a tracking control system which effects a tracking control operation on the basis of the phase of the signal reproduced from tracks recorded on a magnetic recording medium during the reproduction operation.
2. Description of the Prior Art
Generally, in a magnetic recording and reproducing system, such as a video tape recorder (hereinafter referred to as a VTR), the quality of the reproduced signal deteriorates if there is a deviation between the position of the recorded track, which is produced as the recording magnetic head traces the magnetic recording medium during the recording operation, and the position of the reproducing magnetic head as the latter traces the recording medium during the reproduction operation (hereinafter referred to as tracking error). In order to eliminate this tracking error, it is necessary to effect a tracking control operation. For example, in a VTR where the video signal is recorded and reproduced by using a rotary magnetic head assembly, the aforementioned tracking control operation may be performed as a capstan servo-control operation with respect to a capstan motor, the latter of which drives a magnetic tape at a constant speed in response to the tracking error. Another way of effecting such tracking error correction has been to provide an automatic-tracking control system which uses a wobbling or dithering signal, and in which the position of the reproducing magnetic head is controlled so as to maximize the level of the envelope of the reproduced signal, while imparting a slight vibration to the reproducing magnetic head by means of a deflector on which the head is mounted.
With the aforementioned capstan servo-control system, however, optimum reproduction of the video signal may be impossible due to deviation between the position of the control signal track and the position of the video signal track, caused by various reasons. For example, one reason for such deviation may be the result of a misalignment or mounting error which occurs when a control track recording and reproducing head is mounted in each VTR. In this manner, the aforementioned problem arises when signals are recorded with different VTRs. Another reason for such deviation may be due to the elongation or contraction of the magnetic tape due to temperature and/or mechanical variations. Further, if the recording tracks are of a curved configuration, satisfactory operation of the capstan servo-control system further results in a deterioration in the quality of the video signal reproduced. With the tracking control correction effected by use of a wobbling signal, although it is possible to substantially always correctly trace the center of the video track, the effective envelope level of the reproduced signal is reduced to about 90% by such wobbling, whereby deterioration of the overall signal-to-noise ratio inevitably results.